Production of acetic acid by methanol carbonylation is known. See U.S. Pat. No. 5,817,869. In the current acetic acid production process, a reaction mixture is withdrawn from the reactor and is separated by a flash tank into a liquid fraction comprising the catalyst and the catalyst stabilizer and a vapor fraction comprising the acetic acid product, methanol, carbon dioxide, water, methyl iodide, and impurities generated during the carbonylation reaction. The liquid fraction is then recycled to the carbonylation reactor. The vapor fraction is passed to a so-called “light-ends distillation.” The light-ends distillation separates acetic acid from other components and produces a crude acetic acid product. The crude acetic acid product is passed to a drying column to remove water and then is subjected to a so called “heavy-ends distillation” to remove the heavy impurities such as propionic acid.
In the current process, the flash tank does not have a distillation column for the vapor-liquid separation. Thus, the catalyst can be entrained into the flash vapor stream. Deposits of solid catalyst have been seen in downstream equipment. Even though the majority of this catalyst is recovered when cleaning during major shutdowns, major shutdowns are usually three years apart. In the interim, process equipment becomes catalyst inventory storage equipment. Additionally, as catalyst plates out in downstream equipment, it must be replaced upstream with fresh catalyst.
Thus, a new process for producing acetic acid is needed. Ideally, the process reduces the catalyst entrainment in the vapor stream from the flash tank.